Electro-magnetic stepping motor system



Oct. 20, 1964 P. KORDA ELECTRO-MAGNETIC STEPPING MOTOR SYSTEM 2 Sheets-Sheet 1 Filed May 31, 1961 INVENTOR Pau/ Korda WWW A Tram/E7 Oct. 20, 1964 P. KORDA 3,153,755

ELECTRO-MAGNETIC STEPPING MOTOR SYSTEM Filed May 31. 1961 2 Sheets-Sheet 2 lNl ENTOR Pau/ Korda 5 ATTORNEY United States Patent 3,153,755 ELECTRO-MAGNETIC STEPPING MOTOR SYSTEM Paul Korda, Burlingame, Calif., assignor to Ferguson Radio Corporation Limited, London, England, a British company Filed May 31, 1961, Ser. No. 113,932 2 Claims. ((11. 318-134) The present invention relates to rotary tuners, that is to say tuners used in radio receivers, primarily television receivers, for the purpose of tuning to a selected one of a number of channels, the tuner having a turret or disc, hereinafter referred to as a turret, which is rotatable between a number of positions in each of which one or more tuned circuits appropriate to one of the channels are switched into the circuit of the receiver.

It is an object of the present invention to provide im proved means for operating the turret of a rotary tuner and which, in particular, enable the turret to be operated by one or more push buttons (instead of by manual rotation of the tuner knob or spindle) and therefore facilitate remote control without the provision of complex additional apparatus.

According to the present invention there is provided a rotary tuner and means for operating the turret thereof in a radio receiver having a power supply stage including a smoothing choke, the said means comprising an armature disposed adjacent the choke, the armature being resiliently biased away from the choke but in normal operation of the receiver being magnetically drawn towards the choke, a ratchet wheel coupled to or forming part of the turret, a pawl for operation of the ratchet wheel coupled to the armature and a low resistance circuit ineluding a switch for short-circuiting the choke, the arrangement being such that each time the short circuit is completed and broken the armature moves away from and back towards the choke and, as the armature moves back towards the choke, the pawl rotates the ratchet Wheel, whereby the turret moves through a predetermined angle.

The choke therefore performs a dual function: it smooths the power supply and acts as a stepping motor magnet.

It is to be understood that the low resistance circuit for short-circuiting the choke is not necessarily of negligible resistance. Indeed, it is desirable that the circuit should be of suflicient resistance to limit the current drawn when the short circuit is completed to an acceptable level. The condition which must be met is that, when the short circuit is completed, insuflicient current flows through the choke for the armature to be drawn towards the choke against the resilient bias.

When the turret moves through the said predetermined angle it may be said to move one step. It may be arranged that movement of one step is sufiicient to move the turret from one of the said positions to the next one of the said positions. This is preferably the case if the user is to be required tocomplete and break the short circuit (by operation of the said switch) once for each step of movement. As will hereinafter be explained, such a requirement can be avoided and it is possible and sometimes desirable for a plurality of steps of movement of the turret to be necessary to bring it from one position to the next.

The said means can be arranged to be self-stepping by including a further switch in the low-resistance circuit, the further switch being mechanically coupled to the armature and opened only when the armature moves away from the choke, whereby, so long as the short circuit is otherwise completed, the further switch causes the l short circuit to be completed and broken alternately and the turret to be moved by a succession of steps.

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It may then be arranged that the stepping motion is automatically terminated when the selected position is reached. Thus the turret may include or be coupled to a rotary switch which breaks the short circuit when the selected position is reached.

In one embodiment the low-resistance circuit comprises a plurality of parallel paths corresponding to the positions respectively of the turret from which one is to be selected, the said further switch being in series with the said paths, each path comprising a manually operable switch and being completed in part through a rotary switch coupled to or including the turret, the rotary switch being such that, on selection of a given position by closure of the corresponding manually operated switch, the further switch causes the turret to be moved stepbystep until the selected position is reached, whereupon the short circuit is interrupted by the rotary switch and the further switch cannot give rise to further stepping.

The invention will now be described by way of example with reference to the accompanying drawings.

FIG. 1 is a diagram of a mechanism for stepping the turret of a rotary tuner,

FIG. 2 is a diagram of a circuit for controlling the mechanism shown in FIG. 1,

FIG. 3 is a diagram of a simplified controlling circuit for use when selection is required between two positions only, and

FIG. 4 is a diagram of another simplified controlling circuit for use when selection is required between two positions only. A

In FIG. 1 the choke of a television receiver has a Winding 10 on a core 11 of magnetic material. A laminated armature 12 fixed to one end of a lever 13 pivoted at 14 is biased away from theichoke core by means of a tension spring 15 connected between the lever 13 and a support 16. A screw 17 enables the strength of the bias to be adjusted.

The armature is shown at the limit of its travel away from the choke core. This limit is determined by means of an adjustable stop screw 18 against which a block 19 of nylon on the lever 13 bears. The block of nylon reduces noise when the armature moves away from the core 11. For the same reason the face of the armature 12 which is drawn against the core 11 on energisation of the choke is covered with nylon 20, which also determines the gap between the core and armature appropriate to the normal function of the choke as a smoothing element.

A hooked lever 21 is pivoted to the end of the lever 13 remote from the armature 12. The hooked end 22 of the lever 21 forms a pawl urged into engagement with a ratchet wheel 23 by means of a tension spring 24. The ratchet wheel is fixed to the spindle 25 of the turret of a rotary tuner.

When the choke winding 10 is energised the armature 12 is drawn towards the core 11 and the pawl 22 pulls the ratchet wheel 23 round by one step, corresponding to one tooth of the wheel, in the clockwise direction. A spring detent 26 prevents rotation in the anti-clockwise direction. In order to ensure that the extent of the motion is exactly one tooth of the wheel the travel of the pawl is limited in one direction by the screw 18 and in the other by a back stop 27, of nylon to' reduce noise. The back stop 27 is so shaped that the pawl 22 jams between it and the wheel 23 at the desired limit of motion but not to jam so tightly that return of the pawl is interfered with under the action of the spring 15.

These measures are fully sufficient to define the positions of the turret accurately and the conventional springloaded detent, necessarywhen the turret is rotated by hand, is not provided. If provided the detent would only Patented Oct. 20, 1964 e 3 increase the force required to rotate the turret and hence increase the size of the armature.

The turret has 13 different positions and the wheel 23 has 3 l3=39 teeth. Three stepping motions are required therefore to bring the turret from one position to the next. The advantage of using such small steps is that the mass of the armature 20 and other parts can be reduced. It has been found possible to obtain a complete rotation of the turret in approximately three to four seconds. If larger steps and hence larger moving masses were used the phenomenon of mechanical resonance is liable to be troublesome at such a speed of rotation and a slower speed would have to be used. Good results have also been obtained using a larger number of even smaller stepsfor example four teeth per position instead of three.

In normal operation the armature is drawn against the choke core. When it is desired to change the position of the turret a short circuit across the choke is completed and broken once for each step of movement. Whilst this may be done entirely by manual operation of a switch, the circuit of FIG. 2 enables automatic stepping to the selected position to be achieved. To this end the said circuit comprises a switch 30 shown also in FIG. 1 with a fixed contact 31 and a moving contact 32. The moving contact bears an extension 33 which is engaged by the block 19 to open the switch (as shown) when the armature 12 moves away from the core 11. In FIG. 2 the circuit of this switch is shown as being made through the armature 12.

Turning then to FIG. 2 the elements of the conventional power supply circuit, including the choke, of a television receiver, are indicated at 35. The various stages of the receiver constitute the load of the circuit 35 and are indicated symbolically by a resistor 36 which draws a current of about 280 to 300 ma. in normal operation of the receiver. This current through the choke is adequate to overcome the spring 15 and pull the armature 12 against the core 11.

A rotary switch comprises a conducting disc 37 fixed mechanically to the turret spindle 25 but insulated electrically therefrom. One side of the choke winding is permanently connected to this disc by means of a wiping contact 38. Thirteen further wiping contacts 39 corresponding to the thirteen positions of the turret are spaced equidistantly round the disc 37. The disc 37 has a cutout portion 40 such that in each position of the turret one of the contacts 39 does not contact the disc. For any selected position of the turret it is the contact 39 corresponding to that position which does not contact the disc 37.

Only a small number, in Great Britain usually three, of the possible positions of the turret are actually required and only the contacts 39 corersponding to these positions are made use of. Thus three of the contacts 39 are shown connected to the moving contacts of three switches 41, 42 and 43 respectively. The fixed contacts of these switches are all connected through a curent limiting resistor 44 and the switch 30 to the other side of the choke winding 10. The resistor 44 limits the current through the short circuit made across the choke.

When it is desired to select the turret position corresponding to any one of the switches 41, 42 and 43 that switch is closed. The switches are interlocked push-button switches such that when any one is closed it releases any other switch which was closed previously and itself remains closed. In the drawing the switch 43 is closed and the turret is in the position corresponding to that switch. No short circuit across the choke can be made through the switch 43 because the contact 39 connected thereto does not contact the disc 37.

Assume that it is desired to select the position corresponding to the switch 41. This switch is closed, whereupon a short circuit across the choke is made through the switch 41, the switch 30 and the rotary switch comprising the disc 37. The armature 12 thereupon moves away from the core 11, but in so doing opens the switch 30. The armature 12 is therefore drawn back towards the core 11 and the turret is pulled round one step. This cycle of operations repeats however because, on the armature moving back towards the core, the switch 30 is reclosed. The mechanism continues to step the turret round therefore until the selected position is reached when the cut-out 40 in the disc 37 comes round to the contact 39 connected to the switch 41.

When the set is switched off the armature is of course pulled away from the choke core. On switching on again the turret is pulled round one step. This completes the shorting circuit through whichever one of the switches 41 to 43 happened to be depressed when the set was switched on. The turret therefore steps round automatically to the position corresponding to the depressed switch.

The switches 41 to 43 can clearly be housed in a remote control unit. The only connection that need be made between the switches and the receiver can be by way of a cable having three wires individual to the switches and a common return valve. If it is required to change the three positions to be used the service engineer has only to connect the leads from the moving contacts of the switches 41 to 43 to the wiping contacts 39 appropriate to the new positions.

It will be appreciated that the mechanism requires only a few simple mechanical and electrical parts in addition to the parts already necessary in the receiver.

The circuit shown in FIG. 3 is very similar to that shown in FIG. 2 and need not be described in detail. The circuit is for use when only two positions are required and only the contacts 39 appropriate to these two positions are shown. The switches 41 to 43 are replaced by a two-way single pole switch 45. The fixed contacts of this switch are connected to the contacts 39 respectively whilst the moving contact is connected through the resistor 43 to the switch 30. It will be apparent from the foregoing description of FIG. 2 that the two settings of the switch 45 will lead to the automatic selection of the two positions respectively.

Another circuit for use when only two positions are required is shown in FIG. 4. In this the rotary switch and switches 41 to 43 or switch 45 are replaced by a microswitch 46 and a cam operated switch 47 in parallel. The cam 48 for operating the switch 47 is fixed to the spindle 25 and has two indentations 49 and 50 at locations corresponding to the two positions. The moving contact of the switch 47 bears a cam follower 51 which bears against the edge of the disc and can enter the indentation 49 or 50. When the cam follower enters fully one of the indentations the switch 47 opens but is otherwise closed.

As shown the position corresponding to the indentation 49 is the selected position. If it is desired to select the other position the microswitch is depressed momentarily. The turret is therefore moved round by one step. In this however the switch 47 is closed and stepping continues automatically under the action of the switch 30 until the cam follower 51 enters fully the indentation 50. A subsequent depression of the microswitch will lead to stepping until the cam follower again enters the depression 49.

I claim:

1. In a receiver, the combustion of a rotary tuner turret disc, a power supply provided with a smoothing choke, and means for rotating the turret comprising an armature disposed adjacent the choke, said choke being formed to hold the armature in proximity thereto during energization, means for moving said armature away from the choke during deenergization thereof, a ratchet wheel coupled to the turret, a pawl engaging said ratchet wheel formed and positioned to move in response to movement of said armature, and a low resistance circuit shunting the choke and including a switch, said switch having an arm movablfi between a closed choke shunting position and an open position whereby open and closed movement cycle of said switch arm imparts a prescribed rotational movement of said turret disc.

2. In a receiver, the combination of a rotary tuner turret disc, a power supply provided with a smoothing choke, and means for rotating the turret comprising an armature disposed adjacent the choke, said choke holding the armature in proximity thereto during energization, means for moving said armature away from the choke during deenergization thereof, a ratchet wheel coupled to the turret, a pawl engaging said ratchet wheel formed and positioned to move in response to movement of said armature, and a low resistance circuit shunting the choke including a first switch, said switch having an arm movable between a closed choke shunting position and an open position, and a second switch serially connected with the first switch formed to provide an arm movable in respone to the movement of said armature whereby said first and second switches, when serially closed, shunt the armature.

References Cited in the file of this patent UNITED STATES PATENTS 1,341,657 Miller June 1, 1920 1,709,377 Sperry Apr. 16, 1929 2,271,968 Creager Feb. 3, 1942 2,316,899 Stolzenberg Apr. 20, 1943 2,384,114 Moore Sept. 4, 1945 2,388,748 Kopetzky Nov. 13, 1945 2,422,212 Shunn June 17, 1947 2,473,907 Ridgely June 21, 1949 OTHER REFERENCES Marcus and Levy: Elements of Radio Servicing, pp. 94, 95, 323, McGraw-Hill, New York, 1947.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,153,755 October 2O 1964 Paul Korda It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 64, for "combustion" read combination Signed and sealed this 13th day of April 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER htvsting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,153,755 October 2O 1964 Paul Korda I It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 64, for "combustion" read combination Signed and sealed this 13th day of April 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

2. IN A RECEIVER, THE COMBINATION OF A ROTARY TUNER TURRET DISC, A POWER SUPPLY PROVIDED WITH A SMOOTHING CHOKE, AND MEANS FOR ROTATING THE TURRET COMPRISING AN ARMATURE DISPOSED ADJACENT THE CHOKE, SAID CHOKE HOLDING THE ARMATURE IN PROXIMITY THERETO DURING ENERGIZATION, MEANS FOR MOVING SAID ARMATURE AWAY FROM THE CHOKE DURING DEENERGIZATION THEREOF, A RATCHET WHEEL COUPLED TO THE TURRET, A PAWL ENGAGING SAID RATCHET WHEEL FORMED AND POSITIONED TO MOVE IN RESPONSE TO MOVEMENT OF SAID ARMATURE, AND A LOW RESISTANCE CIRCUIT SHUNTING THE CHOKE INCLUDING A FIRST SWITCH, SAID SWITCH HAVING AN ARM MOVABLE BETWEEN A CLOSED CHOKE SHUNTING POSITION AND AN OPEN POSITION, AND A SECOND SWITCH SERIALLY CONNECTED WITH THE FIRST SWITCH FORMED TO PROVIDE AN ARM MOVABLE IN RESPONSE TO THE MOVEMENT OF SAID ARMATURE WHEREBY SAID FIRST AND SECOND SWITCHES, WHEN SERIALLY CLOSED, SHUNT THE ARMATURE. 